1. Field of the Invention
This invention relates to a recording and/or reproducing apparatus for a recording medium in the form of a tape, and more particularly to a recording and/or reproducing apparatus of the reel drive type wherein the speed of rotation of a reel is controlled to feed a recording medium in the form of a tape at a fixed speed and a method of controlling the recording and/or reproducing apparatus.
2. Description of the Related Art
Recording and/or reproducing Apparatus wherein, for example, a magnetic tape accommodated in a tape cassette housing or an open reel tape is employed as a recording medium are well known. In the recording and/or reproducing apparatus- normally a capstan and a pinch roller are contacted with a magnetic tape and the speed of rotation of the capstan is controlled to rotate at a fixed speed to feed the magnetic tape at a fixed speed.
In order to realize feeding of the tape at a fixed speed in a recording and/or reproducing apparatus of the reel drive type, it is one of several possible measures to detect the speed of feeding of the tape and perform velocity servo control of a reel motor in response to the detected speed. A suitable means to detect the tape feeding speed involves employment of a rotary encoder having a roller which contacts and is rotated by the tape when the tape is fed.
By the way, in a recording and/reproducing apparatus of the reel drive type, when the take-up side reel (reel spindle meshed with the take-up side reel) is driven to rotate at a fixed speed. the diameter of the tape wound on the reel varies gradually, and consequently the load to the tape varies and the tape feeding speed varies. While depending upon the length of the tape, the tape feeding speed immediately before the tape is taken up completely sometimes varies, for example, by two times or more compared to that immediately after feeding of the tape is started from its starting end.
Accordingly, even where a same recording medium is used, it is not compatible both with recording and/or reproducing apparatus of the reel drive type and recording and/or reproducing apparatus of the capstan type, which are well known at present. Further, a recording and/or reproducing apparatus of the reel drive type is not suitable as a recording and/reproducing apparatus for which fidelity in sound quality is required since the frequency characteristic and the S/N (signal to noise) ratio are varied from the starting end to the last end of the tape by the variation of the tape feeding speed. For those reasons, recording and/or reproducing apparatus of the reel drive type have a problem in that they are not suitable for practical use while they have an advantage in that they are simplified in construction due to absence of a capstan.
For example, a recording and/or reproducing apparatus is disclosed in Japanese Patent Laid-Open No. Heisei 3-134848 wherein a rotating roller is contacts a magnetic tape and a reel is driven in response to the difference between a period of rotation of the rotating roller and a reference period of rotation for the rotating roller without using a capstan and a pinch roller.
When the tape stops, naturally a reel must stop, and therefore, in order to realize fixed speed feeding of the tape with a recording and/or reproducing apparatus of the reel drive type. upon starting the feeding of the tape, rotation of the reel must be raised rapidly to the speed for fixed speed rotation.
In addition, it is not possible for the reel to continue its rotation at a fixed speed like a capstan when the recording and/or reproducing apparatus is in a stopped condition, and from the necessity for the rising operation, much time is required until the feeding of the tape reaches the predetermined speed. This gives rise to such serious problems as failure in recording at a starting end and a variation in musical interval upon reproduction.
Further, even during recording or reproduction. when the tape feeding speed is displaced by a significant amount from the predetermined speed, much time is required for recovery, resulting in such problems as failure in recording at a starting end and a variation in musical interval upon reproduction.
Further, when it is tried to realize fixed speed feeding of the tape with a recording and/or reproducing apparatus of the reel drive type, it is one of available measures to detect the tape feeding speed and control the speed of rotation of the reel motor by servo control.
However, the tape feeding speed is not always detected precisely due to vibrations applied to the apparatus from the outside, a momentary variation of the operating voltage or an influence of irregularity in thickness. wrinkles and so forth of the magnetic tape. Thus, it is a problem that rotation of the reel motor is liable to be placed out of control by an error in detection of the tape feeding speed arising from some of the factors just described. Accordingly, it is difficult to realize fixed speed feeding that makes use of a rotational servo mechanism.
One of possible means for detecting the tape feeding speed involves a rotary encoder having roller which contacts with and is rotated by the tape so that pulses are generated from the rotary encoder.
In this instance, where the rotary encoder is constructed so as to generate a large number of pulses during one rotation of the roller, a high resolution is obtained so that information of the tape feeding speed is obtained at a short interval of time and servo control of a high reliability is obtained. However, the construction requires a large size for the tape feeding speed detecting means and particularly for the roller and the pulse generating means. which is not preferable.
On the other hand, where the rotary encoder is constructed so as to generate one pulse or a small number of pulses for one rotation of the roller, reduction in size of the tape feeding speed detecting means can be achieved, but since information of the tape feeding speed can be obtained only at a comparatively long interval of time, control of a high reliability cannot be achieved and a delay in servo control may result.
Further, even during recording or reproduction, when the tape feeding speed is displaced by a significant amount from the predetermined speed, much time is required for recovery. resulting in such problems as failure in recording at a starting end and a variation in musical interval upon reproduction.
Furthermore, when the speed is detected by means of the rotary encoder, a slip between the tape and the roller makes it difficult to detect the speed accurately. Accordingly, there is a problem in that it is difficult to achieve accurate servo control.
For example, if the back tension of the supply side reel is insufficient, the contacting pressure or the contacting area between the roller and the tape is rendered unstable so that a slip may occur between the roller and the tape.
On the other hand, when it is tried to obtain sufficient back tension of the supply side reel to eliminate such a possible slip as described above, then complication of the structure, increased torque of the take-up side reel and employment of a motor of a large size and a high power for such torque, increased power dissipation and so forth are involved.
Further, a rise of the slip torque may result in damage to the tape.